The invention is directed to an apparatus for the implementation of plasma etching processes, particularly of reactive ion etching processes, comprising a reaction chamber, a first electrode and a second electrode.
Plasma-assisted processes are employed for working flat substrates, such as semiconductor wafers, in the manufacture of integrated electronic circuits. Such processes are referred to as "plasma etching", "reactive ion etching" or "plasma activated, chemical vapor phase deposition".
U.S. Pat. No. 4,209,379 already discloses a gas plasma reactor. According to claim 1 of this patent, the gas plasma reactor is provided with first and second electrodes that are fashioned such that they surround a reaction space that can be evacuated. The first electrode of the U.S. Patent has a series of openings for the admission of reaction gas into the reaction space and has a second series of openings for the discharge of the gaseous reaction products from the reaction space.
The following problems involving such apparatus are presently in the foreground of the art:
1. The substrates must be reproducibly and effectively tempered with optimum heat transmission. The substrates are thereby usually brought into contact with a heatable or coolable surface. The heat transmission is thereby limited by the actual contact surface that is usually too small or, respectively, by a gap between the heatable or coolable surface on the one hand and the substrates on the other hand.
2. As a result of mechanically moved parts within the process chamber, particles can arise that lead to blemishes or voids on the substrates. These blemishes or voids jeopardize the later functioning of parts fabricated from the substrates.
3. The plasma does not fill the entire volume of the process chamber but only a part thereof. The volume of plasma is greatly dependent on the process parameters. Experience has taught that even slight variations in the process parameters, such as pressure, suction power of the vacuum pump, electrical power or the delivery rates of the gases, noticeably modify the volume of the plasma and, thus, the energy density and the concentration of reactive particles over the substrates. The resulting effect is an inadequately concentrated plasma over the surface of the substrates to be processed, and, due to process chambers that are dimensioned with an excessively large volume, the plasma can also form at a farther distance from the substrates without reliably filling a defined volume, such as the process chamber.
The following solutions have been proposed or are being practiced in the current prior art for overcoming these problems:
1. For improving the heat transmission between a tempering surface and the back side of the substrate, it has been proposed to fill the gap between the two contact surfaces with a material, such as vacuum grease, or with oils having a low vapor pressure, as employed in rotary vane pumps. However, the plasma can be disadvantageously contaminated with the material. As an alternative, the employment of gases as heat-transmitting medium between the two contact surfaces has been disclosed in U.S. Pat. No. 4,514,636; U.S. Pat. No. 4,261,762; and U.S. Pat. No. 4,579,623. However, a precise monitoring of the admission of the heat-transmitting gas is necessary, as is a separate fixing of the substrate. Separate fixing can be particularly disadvantageous for the treatment of lightweight substrates, such as silicon wafers.
Another way of improving the heat transmission between the two contact surfaces is by pressing the substrates against the tempering surface. For example, this can be accomplished by electrostatic attraction of the substrate against the tempering surface, as disclosed in U.S. Pat. No. 4,399,016. According to this patent, this method requires excellent dielectric layers on the tempering surface, which is difficult in practice. It is, therefore, more common to execute the pressing of the substrate with mechanical means, such as claws or pins, or rings actuated with spring pressure, as disclosed in U.S. Pat. No. 4,367,114. These mechanical means, however, frequently effect local inhomogeneities of the plasma that lead to a non-uniform processing of the substrate. Furthermore, pressing means actuated by spring pressure tend to create a pressing power that is inadequately reproducible.
2. Due to abrasion, the known mechanical means for pressing a substrate against a tempering surface produces particles that can proceed onto the substrate. In one type of system, in order to keep particles away from the surface of the substrate to be treated, the substrate is oriented having its surface to be processed facing down. The substrate is pressed against the upper electrode of what is referred to as a parallel plate reactor. This structure, however, makes the loading of the process chamber considerably more mechanically involved.
3. For concentrating the plasma close to a substrate to be processed, U.S. Pat. No. 4,209,357 discloses a small process chamber that allows a reliable definition of the plasma volume. Means for pressing the substrate against a tempering support, however, are not provided.
It is, therefore, new to the art to provide an apparatus for the implementation of plasma etching processes that: provides a reliable and reproducible temperature control of flat substrates to be processed by mechanically pressing these substrates against a tempering surface; prevents particles produced by abrasion of the pressing mechanism from proceeding onto the surface of the substrate; concentrates the plasma in a defined volume close to the substrate to be processed without local inhomogeneities of the plasma occurring; provides means to adjust exhaust gas flow; provides for easy adaptation to adjust anode effective area; and provides for easy adaptation of the reactive gas delivery and distribution system to comply with select operating conditions.